Relocation Read-Only (or RELRO) is a security measure which makes some binary sections read-only.
This means that you are unable to write or execute functions in these ‘binary sections’.
RELRO can be Partial or Full. We will focus more on Full RELRO for the entirety of this tutorial series.
Partial RELRO is the default setting in GCC, and nearly all binaries you will see have at least partial RELRO.
From an attackers point-of-view, partial RELRO makes almost no difference, other than it forces the GOT to come before the BSS in memory.
Full RELRO makes the entire GOT read-only
This prevents us from being able to carry out certain exploits, which we will cover later on in this series.